Dome tact switches are commonly used with short travel keyboards. They give a tactile feedback to a user, are compact, and are discrete. These switches have hard electrical conductors, such as stamped beryllium copper, that are soldered to a circuit board or other substrate material. Unfortunately, dome switches fracture over time and are not normally sealed offered as a normally closed switch. Magnetically coupled pushbutton switches, on the other hand, have a long life and are normally sealed, but the electrical conductors of a magnetically coupled pushbutton switch are printed or painted onto the surface of a substrate. Additionally, a magnetically coupled switch, though thin, has a larger surface area than smaller dome tact switches. There is currently no magnetically coupled pushbutton switch that is a suitable replacement for a dome tact switch primarily because of the differences in electrical conductors and size.
Magnetically coupled pushbutton switches have a metal armature that is normally held spaced from switch contacts by bonded sheet magnet. The switch contacts are usually painted or printed onto the surface of a non-conductive substrate. A non-conductive spacer layer is fixed to the substrate, with an opening in the spacer layer exposing the switch contacts. The sheet magnet overlies the spacer layer. A user-provided actuating force applied to the armature causes it to snap free of the sheet magnet and close the switch contacts by electrically connecting them. Release of the actuating force allows the sheet magnet to attract the armature back to a normal position, in coupled engagement with the sheet magnet so that the armature is spaced from the switch contacts, to reopen the switch. Preferably, the armature has a crown that protrudes through an aperture in the magnet layer. Most often, a polyester membrane layer with suitable graphics overlies the sheet magnet to direct a user of the switch as to location and function of the switch. The benefits of magnetically coupled pushbutton switches have been demonstrated in U.S. Pat. Nos. 5,523,730, 5,666,096, 5,990,772 and 6,069,552, incorporated herein by reference, but not intended to limit the scope of the present invention.
The present invention concerns a method of making a magnetically coupled pushbutton switch that is discrete and may be used in place of a dome tact switch. The method of the current invention includes hard electrical conductors that are uniquely arranged and may be soldered to a circuit board, surface mounted or insert molded. Additionally, the method of the current invention includes many modifications and improvements to a magnetically coupled pushbutton switch that allow the switch to maintain good tactile response even though the switch may be as compact as a smaller tactile dome switch.
A further benefit of the present invention is the ability of the switch to be normally open, normally closed, or both. This capability stems from the unique arrangement of the hard electrical conductors that, in one preferred embodiment, extend over the top of a magnetically coupled switch armature of the present invention. All of the hard electrical conductors are arranged within the switch so that the pushbutton armature of the switch is movable into and out of shorting relationship with the electrical conductors to change the circuit logic for a circuit incorporating the switch. An alternative construction for a normally closed switch of the present invention uses the magnetic attraction of the armature against a magnet to compress spring-loaded normally closed hard electrical conductors against a conductive surface. As used herein, the term xe2x80x9ctopxe2x80x9d refers to that surface of any part in a cross sectional figure of the drawings that faces the top edge of the page, while xe2x80x9cbottomxe2x80x9d refers to that surface of any part in a cross sectional figure of the drawings that faces the bottom edge of the page.